Pot experiment with oat was carried out in the years 2006 – 2007 in greenhouse of IUNG-PIB in Puławy. Three soil moisture objects – optimal soil moisture (60 % water capacity), short drought (60 % water capacity from flowering to full maturity of oat) and long drought (30 % water capacity from tillering to full maturity of oat) and two N rates – 1.2 and 2.4 g/pot were investigated. Soil moisture deficiency influenced negatively on grain yield and all yield components, but positively influenced on total and true protein content as well as share in true protein of albumines, globulines and prolamines. Higher N fertilization level caused grain yield increase (in result of panicle number increase), total and true protein content increase in grain, as well as increasing glutelines share in true protein. Share of remaining protein fractions decreased. Soil moisture and N rates interaction was insignificant.